Resilient athletic shoe soles have been made with a variety of resilient cushioning elements for storing and absorbing impact energy imposed on a wearer's feet. Known shoe soles include fluid bladders that either contain pressurized air or a viscous liquid or gel to absorb shock and store energy.
U.S. Pat. No. 5,406,719, for instance, discloses a bladder that is pressurized with a gas. The bladder includes a heel support with various gas chambers. Gas chambers are located around the perimeter of the heel support, and additional chambers are located centrally in the heel support. The gas confined in the chambers provides cushioning for a foot as gas pressure increases in response to loads applied on the chambers. The patent shows the central chamber communicated with a lateral chamber so that internal gas pressure is equalized between the chambers.
U.S. Pat. No. 5,353,459 also shows a bladder for cushioning a heel. The bladder has a horse-shoe shaped chamber that extends about the periphery of the bladder, from the medial side to the lateral side around the rear of the bladder. Within the horse-shoe shape is a central chamber. As in the '719 patent disclosure, this stiffness of the chambers is controlled by altering the gas pressure therein.
U.S. Pat. No. 4,183,156 discloses an insole shaped insert with interconnected chambers that form pneumatic springs. Two of these chambers are tubular and extend around the sides and back of the heel of the insole. Two additional tubular chambers are disposed between the chambers that extend around the heel sides.
Cushioning bladders that employ a gas or other fluid to cushion shock to a foot suffer from a number of disadvantages. These bladders can usually leak over time, and gas units are especially prone to loss of pressure as the bladder ages. Moreover, the bladders are subject to punctures caused by sharp objects. Once the bladders are punctured, their contents are free to escape, and the bladders cease to effectively cushion shocks. Furthermore, fluid filled bladders also tend to pop and/or compress over time. Most perform significantly differently at different temperatures as the pressure or viscosity of the contained fluids varies. Also, because the fluid within the bladders tends to equalize the pressure within chambers of the bladders, compression of one part of a chamber may merely force the fluid to another part of the chamber decreasing control over localized deformation, and thus cushioning, of the bladder.
Other known soles employ resilient structures that rely on walls of the structure rather that on a fluid contained therein to cushion impact on a wearer's foot. U.S. Pat. No. 5,255,451, for example, teaches a shoe sole with an insert formed from a plurality of undulations. U.S. Pat. No. 4,774,774 shows a midsole formed of a honeycomb structure. Also, U.S. Pat. No. 4,342,158 teaches a sole with a coned disk spring member disposed in the sole heel.